1. Field of the Invention
This invention is directed to making chemical derivatives of carbon nanotubes and to uses for the derivatized nanotubes, including making arrays as a basis for synthesis of carbon fibers.
2. Related Art
Fullerenes are closed-cage molecules composed entirely of sp2-hybridized carbons, arranged in hexagons and pentagons. Fullerenes (e.g., C60) were first identified as closed spheroidal cages produced by condensation from vaporized carbon.
Fullerene tubes are produced in carbon deposits on the cathode in carbon arc methods of producing spheroidal fullerenes from vaporized carbon. Ebbesen et al. (Ebbesen I) xe2x80x9cLarge-Scale Synthesis Of Carbon Nanotubes,xe2x80x9d Nature, Vol. 358, p. 220 (Jul. 16, 1992) and Ebbesen et al., (Ebbesen II), xe2x80x9cCarbon Nanotubes,xe2x80x9d Annual Review of Materials Science, Vol. 24, p. 235 (1994). Such tubes are referred to herein as carbon nanotubes. Many of the carbon nanotubes made by these processes were multi-wall nanotubes, i.e., the carbon nanotubes resembled concentric cylinders. Carbon nanotubes having up to seven walls have been described in the prior art. Ebbesen II; Iijima et al., xe2x80x9cHelical Microtubes Of Graphitic Carbon,xe2x80x9d Nature, Vol. 354, p. 56 (Nov. 7, 1991).
Production of Single-wall Nanotubes
Single-wall carbon nanotubes (SWNT) have been made in a DC arc discharge apparatus of the type used in fullerene production by simultaneously evaporating carbon and a small percentage of VIII B transition metal from the anode of the arc discharge apparatus. See Iijima et al., xe2x80x9cSingle-Shell Carbon Nanotubes of 1 nm Diameter,xe2x80x9d Nature, Vol. 363, p. 603 (1993); Bethune et al., xe2x80x9cCobalt Catalyzed Growth of Carbon Nanotubes with Single Atomic Layer Walls,xe2x80x9d Nature, Vol. 63, p. 605 (1993); Ajayan et al., xe2x80x9cGrowth Morphologies During Cobalt Catalyzed Single-Shell Carbon Nanotube Synthesis,xe2x80x9d Chem. Phys. Lett., Vol. 215, p. 509 (1993); Zhou et al., xe2x80x9cSingle-Walled Carbon Nanotubes Growing Radially From YC2 Particles,xe2x80x9d Appl. Phys. Lett., Vol. 65, p. 1593 (1994); Seraphin et al., xe2x80x9cSingle-Walled Tubes and Encapsulation of Nanocrystals Into Carbon Clusters,xe2x80x9d Electrochem. Soc., Vol. 142, p. 290 (1995); Saito et al., xe2x80x9cCarbon Nanocapsules Encaging Metals and Carbides,xe2x80x9d J. Phys. Chem. Solids, Vol. 54, p. 1849 (1993); Saito et al., xe2x80x9cExtrusion of Single-Wall Carbon Nanotubes Via Formation of Small Particles Condensed Near an Evaporation Source,xe2x80x9d Chem. Phys. Lett., Vol. 236, p. 419 (1995). It is also known that the use of mixtures of such transition metals can significantly enhance the yield of single-wall carbon nanotubes in the arc discharge apparatus. See Lambert et al., xe2x80x9cImproving Conditions Toward Isolating Single-Shell Carbon Nanotubes,xe2x80x9d Chem. Phys. Lett., Vol. 226, p. 364 (1994). While the arc discharge process can produce single-wall nanotubes, the yield of nanotubes is low and the tubes exhibit significant variations in structure and size between individual tubes in the mixture. Individual carbon nanotubes are difficult to separate from the other reaction products and purify.
An improved method of producing single-wall nanotubes is described in U.S. Ser. No. 08/687,665, entitled xe2x80x9cRopes of Single-Walled Carbon Nanotubesxe2x80x9d incorporated herein by reference in its entirety. This method uses, inter alia, laser vaporization of a graphite substrate doped with transition metal atoms, preferably nickel, cobalt, or a mixture thereof, to produce single-wall carbon nanotubes in yields of at least 50% of the condensed carbon. The single-wall nanotubes produced by this method tend to be formed in clusters, termed xe2x80x9cropes,xe2x80x9d of 10 to 1000 single-wall carbon nanotubes in parallel alignment, held together by van der Waals forces in a closely packed triangular lattice. Nanotubes produced by this method vary in structure, although one structure tends to predominate.
A method of producing carbon fibers from single-wall carbon nanotubes is described in PCT Patent Application No. PCT/US98/04513, incorporated herein by reference in its entirety. The carbon fibers are produced using SWNT molecules in a substantially two-dimensional array made up of single-walled nanotubes aggregated (e.g., by van der Waals forces) in substantially parallel orientation to form a monolayer extending in directions substantially perpendicular to the orientation of the individual nanotubes. In this process the seed array tubes are opened at the top (free) end and a catalyst cluster is deposited at this free end. A gaseous carbon source is then provided to grow the nanotube assembly into a fiber. In various processes involving metal cluster catalysis, it is important to provide the proper number of metal atoms to give the optimum size cluster for single wall nanotube formation.
Derivatization of Single-wall Nanotubes
Since the discovery of single wall carbon nanotubes (SWNTs) in 1993 (Iijima, S. and Ichihashi, T., Nature 1993,363:603-605), researchers have been searching for ways to manipulate them chemically. While there have been many reports and review articles on the production and physical properties of carbon nanotubes, reports on chemical manipulation of nanotubes have been slow to emerge. There have been reports of functionalizing nanotube ends with carboxylic groups (Rao, et al., Chem. Commun., 1996,1525-1526; Wong, et al., Nature, 1998,394:52-55), and then further manipulation to tether them to gold particles via thiol linkages (Liu, et al., Science, 1998, 280:1253-1256). Haddon and co-workers (Chen, et al., Science, 1998, 282:95-98) have reported solvating SWNTs by adding octadecylamine groups on the ends of the tubes and then adding dichlorocarbenes to the nanotube side wall, albeit in relatively low quantities (xcx9c2%). While theoretical results have suggested that functionalization of the nanotube side-wall is possible (Cahill, et al., Tetrahedron, 1996, 52 (14):5247-5256), experimental evidence confirming this theory has not been obtained.
Accordingly, it is an object of this invention to provide a method for derivatizing carbon nanotubes, especially the side walls of single-wall carbon nanotubes.
It is another object of this invention to provide a high yield, single step method for producing large quantities of continuous macroscopic carbon fiber from single-wall carbon nanotubes using inexpensive carbon feedstocks at moderate temperatures.
It is yet another object of this invention to provide macroscopic carbon fiber made by such a method. These and other objects of this invention are met by one or more of the following embodiments.
This invention provides single wall carbon nanotubes and/or tubular carbon molecules derivatized with substituents covalently bonded to carbon atoms of the side wall of the nanotube or molecule. The substituents may in principle be attached on the interior and/or exterior of the nanotube side wall, but the attachment will not be predominantly on the exterior wall. In particular, the single wall carbon nanotubes may have substituents selected from fluorine, alkyl and phenyl attached to the side wall. Such single wall carbon nanotubes having fluorine covalently bonded to the side wall of the nanotube demonstrate high electrical resistance.
This invention also provides a method for derivatizing carbon nanotubes comprising reacting carbon nanotubes with fluorine gas, the fluorine gas preferably being free of F2. Where the carbon nanotubes are single wall nanotubes, and the temperature is at least 500xc2x0 C., the product may be multiple wall carbon nanotubes derivatized with fluorine. Where the carbon nanotubes are single wall nanotubes, and the temperature is between 250xc2x0 C. and 500xc2x0 C., the product is single wall carbon nanotubes having fluorine covalently bonded to carbon atoms of the side wall of the nanotube.
In one embodiment, this invention also provides a method for preparing single wall carbon nanotubes having substituents attached to the side wall of the nanotube by reacting single wall carbon nanotubes with fluorine gas and recovering fluorine derivatized carbon nanotubes, then reacting fluorine derivatized carbon nanotubes with a nucleophile. Some of the fluorine substituents are replaced by nucleophilic substitution. If desired, the remaining fluorine can be completely or partially eliminated to produce single wall carbon nanotubes having substituents attached to the side wall of the nanotube. The substituents will, of course, be dependent on the nucleophile, and preferred nucleophiles include alkyl lithium species such as methyl lithium. Alternatively, fluorine may be fully or partially removed from fluorine derivatized carbon nanotubes by reacting the fluorine derivatized carbon nanotubes with various amounts of hydrazine, substituted hydrazine or alkyl amine.
This invention also provides a process for preparing a suspension or solution of single wall carbon nanotubes in various solvents from which individual single wall carbon nanotubes may be isolated, the process comprising providing a mass of single wall carbon nanotubes that include bundles of fibers held in close association by van der Waals forces, derivatizing the side walls of the single wall carbon nanotubes with a plurality of chemical moieties distributed substantially uniformly along the length of said single wall carbon nanotube side walls, said chemical moieties having chemical and steric properties sufficient to prevent the reassembly of van der Waals force bound bundles, producing true solutions and recovering the individual, derivatized single wall carbon nanotubes from said solution or suspension. Preferably, the attached chemical moieties are fluorine to provide solution in various alcohols, preferably isopropyl alcohol, and various R-groups to appropriate to provide solubility in other solvents including CHCl3, Dimethylformamide, etc.
In another embodiment, a method for forming a macroscopic molecular array of tubular carbon molecules is disclosed. This method includes the steps of providing at least about 106 tubular carbon molecules of substantially similar length in the range of 50 to 500 nm; introducing a linking moiety onto at least one end of the tubular carbon molecules; providing a substrate coated with a material to which the linking moiety will attach; and contacting the tubular carbon molecules containing a linking moiety with the substrate.
The present invention also provides seed materials for growth of single wall carbon nanotubes comprising a plurality of single wall carbon nanotubes or short tubular molecules having a catalyst precursor moiety covalently bound or physisorbed on the outer surface of the sidewall to provide the optimum metal cluster size under conditions that result in migration of the metal moiety to the tube end.
This invention also provides a seed array for the catalytic production of assemblies of single wall carbon nanotubes comprising a plurality of relatively short single wall carbon nanotubes assembled in a generally parallel configuration, and disposed on the side wall of each said single wall carbon nanotube a sufficient quantity of physisorbed or covalently bonded transition metal catalyst precursor moieties to provide active catalyst metal atom clusters of the proper size to grow single wall carbon nanotubes under conditions that promote the generation of metal atoms and the migration of said metal atoms to the free ends of said single wall carbon nanotubes.
In another embodiment, a method for continuously growing a macroscopic carbon fiber comprising at least about 106 single-wall nanotubes in generally parallel orientation is disclosed. In this method, a macroscopic molecular array of at least about 106 tubular carbon molecules in generally parallel orientation is provided. The array is processed to provide a single plane of open-ended nanotubes at an angle generally perpendicular to the axes of parallel tubes in the array. The open ends of the tubular carbon molecules in the array are then contacted with a catalytic metal by causing migration of metal atoms released from side wall attached catalyst precursor groups. A gaseous source of carbon is supplied to the end of the array while localized energy is applied to the end of the array in order to heat the end to a temperature in the range of about 500xc2x0 C. to about 1300xc2x0 C. The growing carbon fiber is continuously recovered.
In another embodiment, an apparatus for forming a continuous macroscopic carbon fiber from a macroscopic molecular template array similar to that described above, comprising at least about 106 single-wall carbon nanotubes having a catalytic metal deposited on the open ends of said nanotubes is disclosed. This apparatus includes a means for locally heating only the open ends of the nanotubes in the template array in a growth and annealing zone to a temperature in the range of about 500xc2x0 C. to about 1300xc2x0 C. It also includes a means for supplying a carbon-containing feedstock gas to the growth and annealing zone immediately adjacent the heated open ends of the nanotubes in the template array. It also includes a means for continuously removing growing carbon fiber from the growth and annealing zone while maintaining the growing open end of the fiber in the growth and annealing zone.
The foregoing objectives, and others apparent to those skilled in the art, are achieved according to the present invention as described and claimed herein, and in the text of U.S. provisional application No. 60/106,918, filed Nov. 3, 1998, which is incorporated herein in its entirety.